1. Field of the Invention
The present invention relates to a method for growing semiconductor layers, a method for producing a semiconductor light-emitting element, a semiconductor light-emitting element, and an electronic device. More particularly, the present invention relates to a III-V nitride compound semiconductor light-emitting diode and a variety of apparatus and equipment provided with the light-emitting diode.
2. Description of the Related Art
The existing method for producing a light-emitting diode based on a GaN semiconductor is mostly by growing an n-type layer, an active layer, and a GaN semiconductor layer including a layer on the (0001) plane (or C-plane) of a sapphire substrate by the MOCVD process (Metal Organic Chemical Vapor Deposition), with orientation in the C axis.
Unfortunately, when grown on the (0001) plane (or C-plane) of a sapphire substrate, the pseudomorphic quantum well layer of InGaN oriented in the C axis suffers the disadvantage that a large piezoelectric field occurs in the direction perpendicular to the well plane (or the C axis direction), thereby spatially separating electrons and holes from each other and reducing the probability of electron-hole recombination (which is known as the quantum confined Stark effect). The result is a decrease in internal quantum efficiency in a light-emitting diode based on InGaN/GaN, which in turn leads to a decrease in external quantum efficiency. This is one cause to impede improvement in the light-emitting output.
One way to suppress the quantum confined Stark effect in the active layer is to grow a GaN semiconductor layer with the (11-20) plane (or A-plane) on a sapphire substrate with the (1-102) plane (or R-plane). Unfortunately, the GaN semiconductor layer with the (11-20) plane has many threading dislocations which deteriorate its crystal quality.
There has been proposed in Japanese Patent Laid-Open No. Hei 11-112029 (hereinafter referred to as Patent Document 1) a method for suppressing the quantum confined Stark effect in a semiconductor light-emitting element which is produced by growing a plurality of GaN semiconductor layers including a pseudomorphic quantum well layer. According to the proposed method, the pseudomorphic quantum well layer is grown in a plane direction differing from that in which the piezoelectric field is maximum. In the case where the GaN semiconductor layer has the wurtzite crystal structure, such a plane direction is oblique more than 1° (say, 40°, 90°, or 140°) from the [0001] direction. A semiconductor light-emitting element produced by the foregoing method is shown in FIG. 39. It includes a substrate 101 of SiC or GaN, a buffer layer (not shown) of AlN, a contact layer 102 of n-type GaN, a cladding layer 103 of n-type AlGaN, a multiple quantum well layer 104 of GaInN/GaN or GaInN/GaInN, a cladding layer 105 of p-type AlGaN, and a contact layer 106 of p-type GaN, which are sequentially grown one over the other. The contact layer 102 and the cladding layer 103 are grown in the {0001} plane direction. The multiple quantum well layer 104 is grown on the {2-1-14} plane or {01-12} plane which has been formed by selective growing or selecting etching on the cladding layer 103. The 104a and 104b planes on which the multiple quantum well layer 104 is grown coincide with the {2-1-14} plane or {01-12} plane. The cladding layer 105 and the contact layer 106 change in crystal structure as they grow, with their plane direction switched from that of the multiple quantum well layer 104 to the {0001} plane direction. Incidentally, the reference numerals 107 and 108 denote a p-side electrode and an n-side electrode, respectively.
The existing semiconductor light-emitting element as shown in FIG. 39 permits the multiple quantum well layer 104 as an active layer to decrease in piezoelectric field; however, it suffers the disadvantage that it is not typically easy in practice to grow under good control the multiple quantum well layer 104 with the oblique facet of the {2-1-14} plane or {01-12} plane. Therefore, it presents difficulties in its efficient production.
The present invention was completed to address the foregoing problems. Thus it is an aim of the present invention to provide a method for growing semiconductor layers on a substrate such that the plane direction or the growing plane facet can be selected as desired, or the semiconductor layers can be made to decrease in piezoelectric field and to improve in crystal quality according to need.
It is another aim of the present invention to provide an easy-to-produce semiconductor light-emitting element and a method for producing the same. This aim is achieved by employing the above-mentioned method for growing semiconductor layers at the time of growing the semiconductor layers to form the light-emitting element structure. The resulting semiconductor light-emitting element is identified by good crystal quality of semiconductor layers and reduced quantum confined Stark effect in active layers.
It is further another aim of the present invention to provide a high-performance electronic device equipped with outstanding semiconductor light-emitting elements as mentioned above.